Effect of long-term administration of 4-(dimethylamino)azobenzene on liver cell line derived from rats fed this chemical.

Liver tissue cells derived from rats fed 4-(dimethylamino)azobenzene (DAB) were maintained in vitro for several months. These cells showed higher malignancy after treatment with 4.8 or 19.2 mug/ml of DAB. Subcutaneous back-transplantation of DAB-treated cells showed an earlier appearance of palpable tumors and a higher rate of "take" than the non-treated control cells. The tumor size at 60 days after back-transplantation was also significantly larger in the DAB-treated cells. Long-term treatment with DAB produced few morphological changes of the cells in vitro, but the plating efficiency and resistance to toxic effects of DAB were significantly higher in the treated cells than in the control cells. On the other hand, no definite differences in chromosome number were found between the treated and control cells. These findings suggested that cell malignancy could be promoted by long-term treatment with DAB in vitro